It's faster because there are only a constant number of other faces in a given cell to check to find where the ray exits. Then you can just traverse from cell to cell in this way, without using hierarchical bounding box checks like you normally would.

So its not tree based? Is it a graph traversal of sorts?

Em? Seems reasonable, ray tracing a BVH is inherently slow AF because it diverges like mad(SIMD no like).